The present invention relates to a method for forming ultrasonic three-dimensional images and an apparatus therefor, and more particularly, to a method for forming ultrasonic three-dimensional images on a real time basis using a cross array including two linear phased arrays and an apparatus therefor.
Recent medical ultrasonic scanners for obtaining ultrasonic images uses linear or convex phased arrays containing 256 transducer elements, in order to electronically steer and focus a ultrasonic beam in an image formation plane. The transducer elements forming the array transducers are arranged linearly to only one direction, for example, to an azimuth direction. As a result, such linear phased arrays can be focused in only the azimuth direction, so that only a single plane of an image is provided at a fixed elevation direction (usually 0 degree).
A mechanical scan is performed using a motor in an elevation direction and an electric scan is performed in the azimuth direction, in order to obtain a three-dimensional image using such linear phased arrays. As a result, the image planes constituting a three-dimensional image are obtained from elevational directions differing from each other as necessary in a desired three-dimensional scan area. However, since the beam width in an elevation direction, that is, the thickness of an image plane is fixed by a mechanical lens, a scan time is very long for obtaining a three-dimensional image with respect to a desired area.
When compared with the linear phased arrays, the two-dimensional arrays in which array transducers are arranged in two directions, can perform an electric scan with respect to any direction, thereby enabling dynamic focusing in both an azimuth direction and an elevation direction. Accordingly, the two-dimensional array can provide a more improved image than the linear phased arrays, and enables a more efficient three-dimensional image formation.
However, since the two-dimensional array is generally comprised of the number of transducer elements much more than that of linear phased arrays (typically from 1000 to 4096), the ultrasonic three-dimensional image formation apparatus using the two-dimensional array is unrealistically high in complexity, size and cost. Also, an image scan time consumed for scanning a desired three-dimensional scan area using a two-dimensional array is much longer than a two-dimensional scan time using a linear phased array. For example, when sectional images corresponding to 64 different elevation directions in a desired three-dimensional scan area are required, the two-dimensional array requires an image scan time 64 times that of the linear phased array. Thus, the three-dimensional image formation using the two-dimensional array is limited in its application.